Fuel injection device for a combustion engine

ABSTRACT

The fuel injection device has a fuel-supply pump that delivers fuel from a fuel tank to a high-pressure pump which delivers fuel to a reservoir connected to at least one injector that injects fuel into the internal combustion engine. A fuel filter is disposed between the fuel-supply pump and the high-pressure pump, wherein a return for fuel from the at least one injector and/or from the reservoir to a low-pressure region is provided. The return is provided with an additional fuel filter and downstream of the fuel filter, the return feeds into the connection between the fuel-supply pump and the high-pressure pump.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a 35 USC 371 application of PCT/DE 02/04456 filed onDec. 05, 2002.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention is directed to an improved fuel injection device for aninternal combustion engine.

2. Description of the Prior Art

A fuel injection device of the type with which this invention isconcerned is known from the literature, for exampleDieselmotor-Management, Verlag Vieweg, 2^(nd) edition 1998, p. 262. Thisfuel injection device has a fuel-supply pump that delivers fuel from afuel tank to a high-pressure pump. The high-pressure pump delivers fuelinto a reservoir, which is connected to injectors that inject fuel intothe internal combustion engine. A fuel filter is disposed between thefuel-supply pump and the high-pressure pump. A return is provided foruninjected fuel, leading from the injectors to a low-pressure regionthat is constituted by the fuel tank. The disadvantage here is that thefuel-supply pump must continuously aspirate a large quantity of fuel,part of which must be returned to the fuel tank. The fuel-supply pumpand the fuel filter must therefore be dimensioned as correspondinglylarge and short maintenance intervals for changing the fuel filter arerequired in order to assure that it functions reliably.

SUMMARY AND ADVANTAGES OF THE INVENTION

The fuel injection device according to the invention has the advantageover the prior art that the return of the uninjected fuel into theconnection between the fuel-supply pump and the high-pressure pumprequires a smaller quantity of fuel to be delivered by the fuel-supplypump so that this pump can be dimensioned as correspondingly smaller.The fuel filter can also be dimensioned as correspondingly smaller andthe maintenance intervals for changing it can be extended. An additionalfuel filter in the return assures that the returned fuel and the fuelconveyed back to the high-pressure pump are also sufficiently cleaned.The additional fuel filter here can, in terms of dimensioning and themaintenance intervals required for changing it, be designedindependently of the other fuel filter in accordance with the reducedrequirements since the returning fuel does not contain as manyimpurities as the fuel drawn from the fuel tank. The volume of theadditional fuel filter here can also produce a damping of pressureoscillations and/or pressure surges in the return.

Advantageous embodiments and modifications of the fuel injection deviceaccording to the invention are disclosed. One embodiment assures thatthe fuel-supply pump does not deliver any fuel into the return. Theopening pressure of the check valve can also be used to set the pressurelevel in the return.

BRIEF DESCRIPTION OF THE DRAWINGS

An exemplary embodiment of the invention is described herein below, inconjunction with the drawings, in which:

FIG. 1 schematically depicts a fuel injection device for an internalcombustion engine and

FIG. 2 shows a detail of the fuel injection device according to amodified embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 shows a fuel injection device for an internal combustion engine,for example of a motor vehicle. The internal combustion engine ispreferably an autoignition internal combustion engine and has one ormore cylinders. The fuel injection device has a fuel-supply pump 10 thatcan be disposed inside or outside a fuel tank 12 of the motor vehicle.The fuel-supply pump 10 can have an electric drive motor and draws fuelfrom the fuel tank 12, for example via a prefilter 14. The fuel-supplypump 10 can also be driven, for example, mechanically by the internalcombustion engine or by a high-pressure pump 18 that will be explainedbelow. From the outlet of the fuel-supply pump 10, a connection 16 leadsto the high-pressure pump 18. Between the fuel-supply pump 10 and thehigh-pressure pump 18, the connection 16 is provided with a fuel filter20 embodied as a fine filter through which the fuel delivered by thefuel-supply pump 10 flows. The fuel filter 20 is designed anddimensioned in such a way that the fuel quantity delivered by thefuel-supply pump 10 can pass through it. A maintenance interval forchanging the fuel filter 20 is established so as to assure the functionof the fuel filter 20.

For example, the high-pressure pump 18 has a number of pump elements 19,each of which has a piston that is guided in a cylinder bore and is setinto a stroke motion by a drive unit 17. The drive unit 17 can, forexample, have a camshaft on which the pump pistons of the pump elementstravel, or an eccentric shaft and a polygon that is moved by it, whichsupports the pump pistons. The high-pressure pump 18 is preferablydriven mechanically by the internal combustion engine. The fueldelivered by the high-pressure pump 18 is conveyed to a reservoir 24 viaa connection 23. Each pump element 19 of the high-pressure pump 18 hasan inlet valve 21 that opens into the pump element 19 and through whichfuel can travel from the fuel-supply pump 10 into the pump element 19.Each pump element 19 also has an outlet valve 22 through which fuel canbe displaced out of the pump element 19 and into the reservoir 24. Aninjector 26 is provided for each cylinder of the internal combustionengine and injects fuel into the combustion chamber of the cylinder.Each injector 26 is connected to the reservoir 24 via a connection 28and an electrically triggered valve 30 controls the opening of theinjector 26 for the fuel injection.

The connection 28 between the reservoir 24 and the injector 26 cancontain a pressure booster device that further increases the pressure ofthe fuel supplied to the injector 26 in comparison to the pressureprevailing in the reservoir 24.

In the connection 16 of the fuel-supply pump 10 to the high-pressurepump 18, a fuel metering device 34 is provided, which adjusts the flowof fuel to the high-pressure pump 18. The metering device 34 has anelectrically actuated control valve that is switched by an actuator 36,for example in the form of an electromagnet or a piezoelectric actuator.The actuator 36 is triggered by an electronic control unit 38. Thereservoir 24 is provided with a pressure sensor 40 that is connected tothe control unit 38. The control unit 38 triggers the actuator 36 insuch a way that the fuel metering device 34 adjusts a flow of fuel tothe high-pressure pump 18 that is required in order to maintain a presetpressure in the reservoir 24 by means of the fuel delivered by thehigh-pressure pump 18.

From the connection 16 of the fuel-supply pump 10 to the high-pressurepump 18, upstream of the fuel metering device 34, a connection 48 can beprovided that leads to the drive unit 17 of the high-pressure pump 18,through which a part of the fuel delivered by the fuel-supply pump 10can be supplied to the drive unit 17 to lubricate it. The connection 48preferably contains a pressure valve 50 that opens toward the drive unit17 and unblocks the connection 48 only when a preset pressure isexceeded. The pressure valve 50 assures that particularly duringstarting of the internal combustion engine, if a higher pressure in thereservoir 24 is required and this reservoir must be filled first, thenthe entire quantity of fuel delivered by the fuel-supply pump 10 issupplied to the high-pressure pump 18 and no fuel is diverted forlubricating the drive unit 17. Preferably a throttle restriction 52 isprovided downstream of the pressure valve 50 and limits the flow in theconnection 48. Downstream of the pressure valve 50 and the throttlerestriction 52, a return line 54 can branch off from the connection 48and feed into the connection 16 upstream of the pressure valve 50 andcan contain a throttle restriction 56. Alternatively, the return line 54can also feed into the fuel tank 12.

FIG. 2 shows a different embodiment of the fuel injection device inwhich the connection 48 does not lead to the drive unit 17 region of thehigh-pressure pump 18, but to a return line 80 into the fuel tank 12. Inthis embodiment, the drive unit 17 of the high-pressure pump 18 islubricated in a different way, for example in that the drive unit 17 isconnected to a lubricating oil circuit of the internal combustionengine. If the return line 54 or 80 is fed into the fuel tank 12, thisachieves a balanced, sustained temperature with only slight temperaturedifferences between the fuel in the tank 12 and the fuel in the circuit.

A return 60 leads from the injectors 26 via a line through whichuninjected fuel is diverted. The return 60 from the injectors 26,however, is not conveyed into the fuel tank 12, but feeds into theconnection 16 between the fuel-supply pump 10 and the high-pressure pump18. The return 60 feeds into the connection 16 upstream of the fuelmetering device 34 and upstream of the connection 48. The return 60contains an additional fuel filter 62 and, downstream of this filter,contains a check valve 64 that opens toward the opening of the return 60into the connection 16. The check valve 64 has a valve element 68 loadedin the closing direction by a spring 66 and consequently opens only ifthe force exerted on the valve element 68 by the pressure in the return60 exceeds the force of the closing spring 66. When the pressure in theconnection 16 is higher than in the return 60, the check valve 64prevents fuel delivered by the fuel-supply pump 10 from traveling intothe return 60. The check valve 64 can also be used to maintain a presetpressure in the return 60.

It is possible for the reservoir 24 to be provided with a pressurecontrol valve 70 that opens when a preset pressure in the reservoir 24is exceeded and unblocks an outlet 72 from the reservoir 24, which feedsinto the return 60 upstream of the additional fuel filter 62. It is alsopossible for an outlet 74 to lead from the pressure booster device 32,e.g. for fuel escaping due to a leak in the pressure booster device 32or for a fuel quantity that is required in order to control the pressurebooster device 32, wherein the outlet 74 also feeds into the return 60upstream of the additional fuel filter 62.

The additional fuel filter 62 in the return 60 is embodied as a finefilter; the fuel flowing through the return 60 contains only a fewimpurities from the high-pressure pump 18, the reservoir 24, thepressure booster device 32, the injectors 26, or the connections betweenthem. The design and the maintenance interval of the fuel filter 62 cantherefore be chosen according to these conditions and independently ofthe fuel filter 20. The additional fuel filter 62 in the return can inparticular also be suitably designed in accordance with the relativelyhigh temperature of the returning fuel. The volume of the additionalfuel filter 62 in the return can also damp pressure oscillations andpressure surges that are caused upon termination of the fuel injectionin the injectors 26. This prevents a disadvantageous influence frombeing exerted on the metering device 34 as it adjusts the flow to thehigh-pressure pump 18. The additional fuel filter 62 can also serve as afuel cooler or a separate fuel cooler can be provided in the return 60in order to reduce the temperature of the returned fuel.

The foregoing relates to preferred exemplary embodiments of theinvention, it being understood that other variants and embodimentsthereof are possible within the spirit and scope of the invention, thelatter being defined by the appended claims.

1. A fuel injection device for an internal combustion engine, having afuel-supply pump (10) that delivers fuel from a fuel tank (12) to ahigh-pressure pump (18) via a connection (16), wherein the high-pressurepump (18) delivers fuel to a reservoir (24), which is connected to atleast one injector (26) that injects fuel into the internal combustionengine, having a fuel filter (20) disposed between the fuel-supply pump(10) and the high-pressure pump (18), wherein a return line (60) forfuel from the at least one injector (26) and/or from the reservoir (24)to a low-pressure region is provided, the improvement comprising anadditional fuel filter (62) in the return line (60), downstream of thefuel filter (20), the return line (60) feeding into the connection (16)between the fuel-supply pump (10) and the high-pressure pump (18),wherein the return line (60) contains a check valve (64) that openstoward the opening of the return line (60) into the connection (16). 2.The fuel injection device according to claim 1, further comprising afuel metering device (34) in the connection (16) of the fuel-supply pump(10) to the high-pressure pump (18), the fuel metering device (34)adjusting the flow of fuel from the fuel-supply pump (10) to thehigh-pressure pump (18) in such a way that the high-pressure pump (18)generates a preset pressure in the reservoir (24), the return line (60)feeding into the connection (16) upstream of the fuel metering device(34).
 3. The fuel injection device according to claim 1, furthercomprising a pressure booster device (32) between the reservoir (24) andthe at least one injector (26) for increasing the pressure prevailing inthe reservoir (24), the pressure booster device (32) having an outlet(74) that feeds into the return line (60) upstream of the additionalfuel filter (62).
 4. The fuel injection device according to claim 2,further comprising a pressure booster device (32) between the reservoir(24) and the at least one injector (26) for increasing the pressureprevailing in the reservoir (24), the pressure booster device (32)having an outlet (74) that feeds into the return line (60) upstream ofthe additional fuel filter (62).
 5. The fuel injection device accordingto claim 1, further comprising a fuel cooler in the return line (60). 6.The fuel injection device according to claim 2, further comprising afuel cooler in the return line (60).
 7. The fuel injection deviceaccording to claim 3, further comprising a fuel cooler in the returnline (60).
 8. The fuel injection device according to claim 4, furthercomprising a fuel cooler in the return line (60).
 9. A fuel injectiondevice for an internal combustion engine, having a fuel-supply pump (10)that delivers fuel from a fuel tank (12) to a high-pressure pump (18)via a connection (16), wherein the high-pressure pump (18) delivers fuelto a reservoir (24), which is connected to at least one injector (26)that injects fuel into the internal combustion engine, having a fuelfilter (20) disposed between the fuel-supply pump (10) and thehigh-pressure pump (18), wherein a return line (60) for fuel from the atleast one injector (26) and/or from the reservoir (24) to a low-pressureregion is provided, the improvement comprising an additional fuel filter(62) in the return line (60), downstream of the fuel filter (20), thereturn line (60) feeding into the connection (16) between thefuel-supply pump (10) and the high-pressure pump (18), furthercomprising a pressure booster device (32) between the reservoir (24) andthe at least one injector (26) for increasing the pressure prevailing inthe reservoir (24), the pressure booster device (32) having an outlet(74) that feeds into the return line (60) upstream of the additionalfuel filter (62).
 10. The fuel injection device according to claim 9,further comprising a fuel cooler in the return line (60).